linux/rust
Miguel Ojeda 7a5f93ea58 rust: kbuild: set bindgen's Rust target version
Each `bindgen` release may upgrade the list of Rust targets. For instance,
currently, in their master branch [1], the latest ones are:

    Nightly => {
        vectorcall_abi: #124485,
        ptr_metadata: #81513,
        layout_for_ptr: #69835,
    },
    Stable_1_77(77) => { offset_of: #106655 },
    Stable_1_73(73) => { thiscall_abi: #42202 },
    Stable_1_71(71) => { c_unwind_abi: #106075 },
    Stable_1_68(68) => { abi_efiapi: #105795 },

By default, the highest stable release in their list is used, and users
are expected to set one if they need to support older Rust versions
(e.g. see [2]).

Thus, over time, new Rust features are used by default, and at some
point, it is likely that `bindgen` will emit Rust code that requires a
Rust version higher than our minimum (or perhaps enabling an unstable
feature). Currently, there is no problem because the maximum they have,
as seen above, is Rust 1.77.0, and our current minimum is Rust 1.78.0.

Therefore, set a Rust target explicitly now to prevent going forward in
time too much and thus getting potential build failures at some point.

Since we also support a minimum `bindgen` version, and since `bindgen`
does not support passing unknown Rust target versions, we need to use
the list of our minimum `bindgen` version, rather than the latest. So,
since `bindgen` 0.65.1 had this list [3], we need to use Rust 1.68.0:

    /// Rust stable 1.64
    ///  * `core_ffi_c` ([Tracking issue](https://github.com/rust-lang/rust/issues/94501))
    => Stable_1_64 => 1.64;
    /// Rust stable 1.68
    ///  * `abi_efiapi` calling convention ([Tracking issue](https://github.com/rust-lang/rust/issues/65815))
    => Stable_1_68 => 1.68;
    /// Nightly rust
    ///  * `thiscall` calling convention ([Tracking issue](https://github.com/rust-lang/rust/issues/42202))
    ///  * `vectorcall` calling convention (no tracking issue)
    ///  * `c_unwind` calling convention ([Tracking issue](https://github.com/rust-lang/rust/issues/74990))
    => Nightly => nightly;

    ...

    /// Latest stable release of Rust
    pub const LATEST_STABLE_RUST: RustTarget = RustTarget::Stable_1_68;

Thus add the `--rust-target 1.68` parameter. Add a comment as well
explaining this.

An alternative would be to use the currently running (i.e. actual) `rustc`
and `bindgen` versions to pick a "better" Rust target version. However,
that would introduce more moving parts depending on the user setup and
is also more complex to implement.

Starting with `bindgen` 0.71.0 [4], we will be able to set any future
Rust version instead, i.e. we will be able to set here our minimum
supported Rust version. Christian implemented it [5] after seeing this
patch. Thanks!

Cc: Christian Poveda <git@pvdrz.com>
Cc: Emilio Cobos Álvarez <emilio@crisal.io>
Cc: stable@vger.kernel.org # needed for 6.12.y; unneeded for 6.6.y; do not apply to 6.1.y
Fixes: c844fa64a2 ("rust: start supporting several `bindgen` versions")
Link: 21c60f473f/bindgen/features.rs (L97-L105) [1]
Link: https://github.com/rust-lang/rust-bindgen/issues/2960 [2]
Link: 7d243056d3/bindgen/features.rs (L131-L150) [3]
Link: https://github.com/rust-lang/rust-bindgen/blob/main/CHANGELOG.md#0710-2024-12-06 [4]
Link: https://github.com/rust-lang/rust-bindgen/pull/2993 [5]
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20241123180323.255997-1-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
2024-12-10 01:06:10 +01:00
..
bindings Char/Misc/IIO/Whatever driver subsystem updates for 6.13-rc1 2024-11-29 11:58:27 -08:00
helpers Rust changes for v6.13 2024-11-26 14:00:26 -08:00
kernel block-6.13-20242901 2024-11-30 15:47:29 -08:00
macros Char/Misc/IIO/Whatever driver subsystem updates for 6.13-rc1 2024-11-29 11:58:27 -08:00
uapi rust: map __kernel_size_t and friends also to usize/isize 2024-11-10 23:58:00 +01:00
.gitignore rust: support running Rust documentation tests as KUnit ones 2023-07-19 09:32:53 -06:00
bindgen_parameters rust: map __kernel_size_t and friends also to usize/isize 2024-11-10 23:58:00 +01:00
build_error.rs rust: add build_error crate 2022-12-04 01:59:16 +01:00
compiler_builtins.rs rust: add intrinsics to fix -Os builds 2024-08-10 00:05:10 +02:00
exports.c rust: exports: improve grammar in commentary 2024-10-21 17:35:33 +02:00
ffi.rs rust: use custom FFI integer types 2024-11-10 23:58:00 +01:00
Makefile rust: kbuild: set bindgen's Rust target version 2024-12-10 01:06:10 +01:00